Everything you need to know for Atoms, Bonds and Groups Exam 1 with OCR A

Well. Pretty much everything anyway.

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AS Unit F321: Atoms, Bonds and Groups
Module 1: Atoms and Reactions
1.1.1 Atoms
a) All elements are made up from atoms. Atoms are made up from 3 types of particles, protons,
neutrons and electrons. Electrons have a -1 relative charge, and Protons have a +1 charge, whilst
Neutrons are neutral. Protons and neutrons have a relative mass of 1, whilst electrons have a relative
mass of -12000-.
b) The majority of mass is in the nucleus of the atom, where you find the protons and neutrons, but its
diameter is tiny compared to the diameter of the whole atom.
c) The top number on a nuclear symbol is the mass (nucleon) number, which is the total number of
protons and neutrons in the nucleus. The atomic (proton) number is the number of protons, and is on
the bottom. The neutrons can be found by subtracting the atomic number from the mass number.
d) Negative ions have more electrons than protons, and positive ions have fewer.
e) Isotopes of an element are atoms with the same number of protons but different numbers of
neutrons. It is the number and arrangement of electrons that decides the chemical properties of an
element. Isotopes have the same configuration of electrons so they've got the same chemical
properties. They do have slightly different physical properties due to the change in mass, such as
different densities and rates of diffusion.
f) 12C is used as the standard measurement of relative masses, with one atom of carbon-12 weighing 12.
g) Relative isotopic mass is the mass of an atom of an isotope of an element on a scale where an atom
of carbon-12 is 12. Relative atomic mass (Ar) is the average mass of an atom of an atom of an
element on a scale where an atom of carbon-12 is 12.
h) Relative isotopic abundance and how to work it out from a mass spectrum.
i) Relative Molecular Mass (Mr) is the average mass of a molecule or formula unit on a scale where an
atom of carbon-12 is 12. Relative Formula Mass is used for compounds that are ionic or giant
1.1.2 Moles and Equations
a) The amount of substance is the quantity whose unit is the mole. The amount of substance is measured
using a unit called the mole and given the symbol n. One mole is the amount of any substance
containing as many particles as there are in carbon atoms in exactly 12g of carbon-12 and is equal to
6.02 x 1023 particles. This number is known as the Avogadro constant.
b) Molar mass is the mass per mole of a substance. Its unit is g mol-1.
c) The empirical formula is the simplest whole-number ratio of atoms of each element present in a
compound. The molecular formula is the actual number of atoms of each element in a molecule.
d) Practice calculating molecular and empirical formulae by using composition by mass and percentage
e) A chemical reaction starts with reactants and ends with products. An equation is a symbolic
representation of the reaction taking place.
f) Practice calculations involving mass, gas volume and solution volume and concentration.
g) Stoichiometry is the molar relationship between the relative quantities of substances taking part in a
h) The concentration of a solution tells you how much solute is dissolved in the solvent, measured in
moles per cubic decimetre, dm3 (1000 cm3). A standard solution is a solution of known concentration
and is usually used in titrations to work out information about the other substance. The terms

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Concentrated is a large amount of solute per dm3 and dilute is a small amount. Concentrated acids
usually have a concentration of greater than 10 mol dm3.
1.1.3 Acids
a) Acids release H+ ions (protons) in aqueous solution. H+ ions are the active ingredient in acids. An H+ ion
is responsible for all acid reactions. An acid is a proton donor.
b) Commons acids include sulphuric acid (H2SO4), hydrochloric acid (HCl) and nitric acid (HNO3).
c) Common bases are metal oxides and hydroxides and ammonia.…read more

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a) An oxidation number is a measure of the number of electrons that an atom uses to bond with
atoms of another element. The rules are set out in the table below:
Species Oxidation Number Examples
Uncombined element 0 C,Na,O2, P4
Combined oxygen -2 H2O, CaO
Combined hydrogen +1 NH3,H2S
Simple ion Charge on ion Na+, +1, Cl- -1
Combined fluorine -1 NaF, CaF2
When bonded to fluorine, oxygen had an oxidation number of +2. In peroxides, it has an oxidation number
of -1.…read more

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Module 2: Electrons, Bonding and Structure
1.2.1 Electron Structure
a) The first ionisation energy of an element is the energy required to remove one electron from
each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions. Successive
ionisation energies are a measure of the energy required to remove each electron in turn e.g.…read more

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A sub-shell is a group of the same type of atomic orbital (s, p, d or f) within a shell. The sub-shells
within a shell have different energy levels. Within a shell the sub-shell energies increase in the
order s, p, d and f.
h) The order of sub shells is as follows: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 4d, 4f. Each energy level must
be full before the next, higher energy level starts to fill.…read more

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Predict the shapes of molecules similar to those seen here
k) Electronegativity is a measure of the attraction of a bonded atom for the pair of electrons in a
covalent bond.
l) Because the atoms in some compounds are different, they differ in their Electronegativity. The Cl
atom in a molecule of HCl is more electronegative than the H atom and attracts the pair of bonded
electrons more.…read more

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­ so can thus conduct electricity. Ionic lattices
dissolve in polar solvents, such as water because the solvent surrounds each ion to form a solution.
r) Elements and compounds with covalent bonds are either simple molecular lattices or giant
covalent lattices. Simple molecular structures are made up from small, simple molecules such as
Ne, H2 and H2O. In a simple molecular lattice molecules are held together by weak IMFs with the
atoms within molecules being strongly bonded together by covalent bonds.…read more

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Across each period there is a general increase in the ionisation energy due to the presence of
more protons. Electrons are added to the same shell, so the outer shell is drawn inwards slightly,
reducing the atomic radius, and the electron shielding will not change. At the start of a next
period, a new shell is formed, increasing the distance of the outermost shell from the nucleus and
increasing the electron shielding of the outermost shell by inner shell.…read more

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Disproportionation is a reaction in which the same element is both reduced and oxidised. An
example is the use of chlorine in water to kill bacteria. It reacts with water, forming HCl and HClO,
and it is both oxidised and reduced. In aqueous sodium hydroxide it reacts to form bleach: Cl2
+ 2NaOH goes to NaCl +NaClO + HCl.
d) Fluorine is super reactive! Chlorine is a toxic gas, and can be harmful, so must be used sparingly.…read more


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